July 31, 2010

Ancient Nordic mtDNA (Melchior et al. 2010)

The reduction of mtDNA haplogroup I in modern Scandinavians has been observed before (by the same author). Inferences from the 2 Bell Beaker and 1 Bronze Age samples which belong to U subgroups should be cautious, however these contrast with later groups as well as with the earlier Neolithic Scandinavian TRB samples. Table 5 has haplogroup frequencies in various age-place groups. From the paper:

Table 5 shows the occurrence of haplogroups among ancient Danes and Britons and modern Danes and Scandinavians. Using G-tests, no significant deviations were observed among the extant populations or between the ancient Britons and the ancient Danes, despite the two ancient population samples show a surplus of Hg T and Hg I, respectively. We have previously observed a high frequency of Hg I's among Iron Age villagers (Bøgebjerggård) and individuals from the early Christian cemetery, Kongemarken [16], [17]. This trend was also found for the additional sites reported here, Simonsborg, Galgedil and Riisby. The overall frequency of Hg I among the individuals from the Iron Age to the Medieval Age is 13% (7/53) compared to 2.5% for modern Danes [35]. The higher frequencies of Hg I can not be ascribed to maternal kinship, since only two individuals share the same common motif (K2 and K7 at Kongemarken). Except for Skovgaarde (no Hg I's observed) frequencies range between 9% and 29% and there seems to be no trend in relation to time.

There are two main explanations for the reduction in haplogroup I frequency: (a) negative selection and/or (b) the movement of non-I bearing populations into the region of interest. Unless selection occurred very recently (in the last millennium), the lack of a temporal trend adds some weight in favor of (b) and contra (a).

Of interest:

Several haplogroups which are rare or absent among the extant population of southern Scandinavia were observed. Hg's R0a and U7 have been discussed previously [15], [17]. Here we note the finding of Hg N1a in the Medieval Riisby (Table 3), which seems to be common among early European LBK farmers [10], a rare Hg T2 motif in the Iron Age settlement Simonsborg (Table 2) and Hg U5a and Hg U4 at the Early Bronze Age site Bredtoftegård and Neolithic Damsbo (Table 1).

A main conclusion from this paper is that the mtDNA gene pool does not appear to change "monotonically" with time, as the Neolithic Bell Beaker and Bronze Age groups resemble Mesolithic ones rather than the Neolithic TRB. Thus, it is safe to say that simple one-time admixture scenaria between "Paleolithic" and "Neolithic" gene pools grossly oversimplify reality.

The more we learn about prehistory, the less we can believe in the paradigm of static people changing their subsistence, technology, language from the Paleolithic to the present. Migrationism is overdue for a comeback as an explanatory tool for the plethora of unexpected results that the bones of ancient humans present us with.

The persistence of mtDNA-U gene pools down to the Bronze Age leads the authors to consider the Iron Age as the origin of the modern Scandinavian mtDNA gene pool:

However, the frequency of Hg U4 and U5 declines significantly among our more recent Iron Age and Viking Age Danish population samples to the level observed among the extant Danish population. Our study therefore would point to the Early Iron Age and not the Neolithic Funnel Beaker Culture as suggested by Malmström et al. (2009) [14], as the time period when the mtDNA haplogroup frequency pattern, which is characteristic to the presently living population of Southern Scandinavia, emerged and remained by and large unaltered by the subsequent effects of genetic drift.

I find that a reasonable suggestion, as it was in the Iron Age that the Germanic language group seems to have emerged in southern Scandinavia and northern Germany, and started to experience its demographic expansion that rendered it one of the largest in modern Europe. So, it makes sense that the mtDNA composition of that age would persist down to the present-day inhabitants.

Using established criteria for work with fossil DNA we have analysed mitochondrial DNA from 92 individuals from 18 locations in Denmark ranging in time from the Mesolithic to the Medieval Age. Unequivocal assignment of mtDNA haplotypes was possible for 56 of the ancient individuals; however, the success rate varied substantially between sites; the highest rates were obtained with untouched, freshly excavated material, whereas heavy handling, archeological preservation and storage for many years influenced the ability to obtain authentic endogenic DNA. While the nucleotide diversity at two locations was similar to that among extant Danes, the diversity at four sites was considerably higher. This supports previous observations for ancient Britons. The overall occurrence of haplogroups did not deviate from extant Scandinavians, however, haplogroup I was significantly more frequent among the ancient Danes (average 13%) than among extant Danes and Scandinavians (~2.5%) as well as among other ancient population samples reported. Haplogroup I could therefore have been an ancient Southern Scandinavian type “diluted” by later immigration events.Interestingly, the two Neolithic samples (4,200 YBP, Bell Beaker culture) that were typed were haplogroup U4 and U5a, respectively, and the single Bronze Age sample (3,300–3,500 YBP) was haplogroup U4. These two haplogroups have been associated with the Mesolithic populations of Central and Northern Europe. Therefore, at least for Southern Scandinavia, our findings do not support a possible replacement of a haplogroup U dominated hunter-gatherer population by a more haplogroup diverse Neolithic Culture.

23 comments:

About mtDNA I, in Keyser et al. 2009, about bronze-iron age south Siberian samples, there was one haplogroup mtDNA I and it so happens that it also matched nordic haplotypes:

"Specimen S24 was found to belong to haplogroup I,subclade I4. Exact matches to this I4 type were mainlyfound in northern and eastern Europe individuals. The factthat one ancient Scandinavian specimen (0–400 AD) borethis sequence gives direct evidence of the antique presenceof such sequence in the north of Europe (Melchior et al.2008)"

"If the Neolithic and Bronze Age populations had the same Hg frequencies as extant Danes, the probability of picking by chance three Hg U individuals among them would be x3 = 0.0020, where x is the frequency of Hg U among extant Danes (12.5%)."

As the study says: the likelihood that 3 out of 3 samples would all come out U4/U5, assuming modern U4/U5 frequencies of 12%, is 1 in 500. These are the 3 very ancient samples, from 3,000 to 4,000 years ago. The rest are from 1,000 to 2,000 years ago.

With respect to these more recent samples, they found 53 of them, and 7 belonged to mtdna I, or 13%, while today's frequency of mtdna I in Denmark, or anywhere in Europe, is 2% to 3%. The probability that 7 or more samples would belong to mtdna I in a sample of 53, assuming modern mtdna I frequencies of 2,5%, is 1 in 3,000.

Ergo, barring the 1 in 3,000 longshot possibility that they found 7 mtdna I samples by sheer luck, their results force us to conclude something drastic must have happened to the Danish mtdna genepool in the last 1,000 years. And I mean really drastic, because to accomplish a reduction from 13% to 2,5% requires an almost complete population replacement. Or alternatively, that mtdna I was subject to natural selection starting around 1,000 years ago, for some bizarre reason. And in both cases, the massive reduction remarkably placed the modern Danish frequency of mtdna I at the exact same rate it is found in every other corner of Europe.

I am more doubtful of the selection hypothesis, both because of the lack of a temporal trend, and also because haplogroup I exists at a high frequency today outside of Europe. It's difficult to see a selection hypothesis that would have targeted Nordic I in the last 1,000 years. I could see selection operating e.g., because of the different climate that early I-bearers into Scandinavia faced, or due to the subsistence shift after the early Neolithic, but not at all easy to imagine a selective force that started operating 1,000 years ago.

This is positive selection of mtDNA H, not the fictitious mass migration of Indo-Europeans or intentional population replacement.I don't think this is specifically targeting Nordic populations, as I expect the same happened earlier for the less remote regions of Europe. There may have been more variety of mtDNA in the south which would have acted as negative selection on mtDNA I. Why would the north be the last to be affected by the selection? The main reason is obvious. As an aside the same core sequence was found in the Eulau sample. It seems the full range of I1 ->I4 are found in North/NW Europe even today.

What might be the reason of a possible population replacement in the last 1000 years in Scandinavia? Languages haven't changed much, ethnic identities have remained largely intact. Only religion changed at the beginning of the last 1000 years, might that be the reason? Maybe the early Christian Scandinavian kings imported people from already Christian lands like Germany to increase the number of their Christian subjects. Might that also explain the Germanization (here by "German-" I only mean the language of Germany) of some features of the Scandinavian Germanic languages within the last 1000 years? The frequency of the maternal hg I in today's Germans is also 2.5% (probably even less in the northern parts as it is 3.5% in today's Austrians, who are basically a subset of southern Germans), so my speculations might have some validity.

But such importations wouldn't affect already colonized Iceland and the Faroe Islands, how then their frequency of the maternal hg I has also decreased (4.5% in today's Icelanders)? Their case is much easier to explain: Nordic settlers migrating to Iceland and the Faroe Islands married with Scottish/Irish women on their way and also after the colonization (there were already Gaelic populations living for some time). This has been proven by the recent genetic studies showing Scandinavian paternal haplogroups and Gaelic maternal haplogroups in the majority of Icelanders and the Faroe Islanders. Also the frequency of the maternal hg I in today's Icelanders is 4.5%, it is between the frequency of today's Scotland (5%) and Ireland (3%). I don't know its frequency in today's Faroese (as the details of the Faroese studies aren't openly published), but given the results of the maternal hg studies, it should be close to today's Scottish and Irish frequencies.

If really haplogroups are unequal to fight off some diseases (I remember reading this kind of things several times. I ain't wrong, am I?), is it possible that events such as the black death (The European population was diminished between 30% to 60 %) have a responsability (at least partially) ?

"Positive selection on haplogroup H would have reduced the frequency of non-H haplogroups across the board, not specifically of haplogroup I."

-- Maybe there is some unknown selective pressure against mtDNA I that we have not discovered yet. Keep in mind these are small villages, and Denmark has a meagre 5 million people today in 2010. I would expect distant relationship amongst small villages about 1200 years ago, compared to the more metropolitan atmosphere of medieval Denmark. Perhaps "new blood" was brought in, or various disease have wiped out certain haplogroups. The point is...a scientific explanation is likely the culprit rather than anything romantic suggested by anyone so far.

"This has been proven by the recent genetic studies showing Scandinavian paternal haplogroups and Gaelic maternal haplogroups in the majority of Icelanders and the Faroe Islanders."

-- I'm not sure what their conclusions were based on. Type casting R1b = Irish/Scot and R1a/I1 = Norse? Or did they use autosomal studies? If the latter, it will show you Norway, Denmark, and a lesser extent Sweden have closest affinity to UK/Ireland anyways. How can you prove directional gene flow?

The decline in Danish mtDNA haplotype I would suggest a roughly 80% influx of new Germanic (probably the first Indo-European wave), and 20% old populations (probably pre-Indo-European).

Whatever altered their mtdna had to occur in the Middle Ages >>> The 13% mtdna I results are from 0 AD and 1000 AD, with 24 and 29 samples, respectively, and with frequencies of 13% and 14% for mtdna I.

This is positive selection of mtDNA H, not the fictitious mass migration of Indo-Europeans or intentional population replacement.

This also has a serious problem, because non-H haplogroups, having no selection acting upon them, would diminish uniformly, ergo, mtdna I would still be the 2nd most important haplogroup in Denmark, as it was in 0 AD and 1000 AD. Note that the frequency of mtdna H was about 30%, so an increase to its current rate of 40% or 45% would only bring mtdna I down from 13% to 11%.

Maybe the early Christian Scandinavian kings imported people from already Christian lands like Germany to increase the number of their Christian subjects.

Total population replacement, or even mostly replaced, doesn't mesh with the autosomal results. Thanks to the genetic distances calculated by Heath (2008) and McEvoy (2009), it can be seen that modern Danes are precisely squarely in the middle of their neighbors to the south, north, and west. The FST genetic distance between Denmark and England is barely 0,0004, an amazingly small distance. The English-Romania FST is 0,0024. England-Poland is 0,0027.

the maternal hg I has also decreased (4.5% in today's Icelanders)Nordic settlers migrating to Iceland and the Faroe Islands married with Scottish/Irish womenthe frequency of the maternal hg I in today's Icelanders is 4.5%, it is between the frequency of today's Scotland (5%) and Ireland (3%)

It looks more likely that Iceland's mtdna I frequency simply reflects their Irish and Scottish origins, instead of a decrease from a higher rate back in Scandinavia.

My theory is that the early R1a1a Indo-European populations of the North European plain were influenced by Iron Age migrants from the south, bringing with them R1b. These were, most likely, carriers of the La Tene culture, and their arrival eventually resulted in the formation of the Germanic language group.

The pre-Germanic groups of Northern Europe show links to Eastern Europe, and the blond Kurgan "Europeans" of Central Asia, both in terms of Y-DNA (R1a1a) and mtDNA (lots of close matches). This isn't really surprising, since Corded Ware culture stretched all the way from present day Holland to Russia, and Corded Ware groups (Abashevo) were apparently key players in the formation of the early Indo-Iranians near the Urals.

Eh - I would attribute that language Germanization to the 500 years of Hanse trade connections. It's the most straightforward explanation - and the same that brought many English and later even some Creole words to Northern German harbor areas.

I'm not sure what their conclusions were based on. Type casting R1b = Irish/Scot and R1a/I1 = Norse? Or did they use autosomal studies? If the latter, it will show you Norway, Denmark, and a lesser extent Sweden have closest affinity to UK/Ireland anyways. How can you prove directional gene flow?

A very good example of such studies is Als et al.'s study "Highly discrepant proportions of female and male Scandinavian and British Isles ancestry within the isolated population of the Faroe Islands":

http://www.nature.com/ejhg/journal/v14/n4/full/5201578a.html

It also investigates Icelanders and also compares mtDNA data with Y-chromosome data in Faroese.

Total population replacement, or even mostly replaced, doesn't mesh with the autosomal results. Thanks to the genetic distances calculated by Heath (2008) and McEvoy (2009), it can be seen that modern Danes are precisely squarely in the middle of their neighbors to the south, north, and west. The FST genetic distance between Denmark and England is barely 0,0004, an amazingly small distance. The English-Romania FST is 0,0024. England-Poland is 0,0027.

What is the Fst distance between Germans and Scandinavian ethnicities?

Eh - I would attribute that language Germanization to the 500 years of Hanse trade connections. It's the most straightforward explanation - and the same that brought many English and later even some Creole words to Northern German harbor areas.

My speculations and the Hanseatic League theory (I already knew it) don't necessarily contradict each other. The German importation to Scandinavia might have made trade connections between Germany and Scandinavia much easier.

Not to beat a dead horse - but it's not a theory in the vulgar sense - it is pretty much established and widely-accepted historical account. The Hanse really was (and continued to be, and in some sense still is) an incredibly powerful social agent in the north for half a millennium.

Probable that the great plague is responsible of the change. Scandinavia was devastated from the plague , as other regions of Europe, but it saved others of it, for unknown reasons.The effects of the great plague were lasting and only after two centuries the population still started to growth.

I guess it is much smaller than that between, say, Denmark and north Germany or even between Sweden/Norway (especially Norway) and north Germany.

Not to beat a dead horse - but it's not a theory in the vulgar sense - it is pretty much established and widely-accepted historical account. The Hanse really was (and continued to be, and in some sense still is) an incredibly powerful social agent in the north for half a millennium.

I am sure some details of the linguistic Germanization of Scandinavian languages that are due to the Hanseatic Leage are well documented. But I guess most of the details of the linguistic Germanization of Scandinavian languages aren't so clear from linguistic history, so for them there is room for possibilities other than the Hanseatic connection (like my above speculation).

The interesting things happening historically around 1000 CE in the region include the Norman Conquest, the Little Ice Age, Leif Erickson's colonization of North America and its failure, and Viking coastal invasions. There was a lot of out migration at the time, possibly driven by the Little Ice Age's impact on crops which was probably more extreme at the climate extremes than in places with moderate climates.

One of the discoveries that has been made historically, as sources have expanded beyond European ones to cover both sides of conflicts, is that a lot of the famous waves of invasions (e.g. the Sea People invasions at the end of the Bronze Age, the Huns into Rome, and the Uralic speaking people's invasion that lead to Hungary much later), is that a lot of historic invasions had more of a "push" motive than a "pull" motive. So, the inference that "something was rotten in Denmark" and the vicinity around 1000 CE, pushing people to look for greener pastures, isn't an unreasonable one.

The Christianization factor is also plausible.

I'd be inclined to see a decline in hap I on a population basis, if due to selection, rather than in-migration (with in-migration perhaps from captives gathered up in Viking raids), to be a product of population structure in the area, rather than true genetic trait based selection. For example, perhaps people with hap I were predominantly crop farmers, while people with different haps tended to be hunters, fishers, herders and raiders. If crop farming were bad for a few generations (as it was in Ireland during the potato famine, and in Sicily at around the same time), and crop farmers had to starve or migrate to better locations, this would look like selection, although the coincidence of hap I genes and the fact that they were from a population that ended up crop farming in Scandinavia didn't flow from any hap I associated traits.

Just a last comment. We talk about extinction of mtDNA I, but do we see any mtDNA signatures among the T2's J's and so forth which are present in ancient samples but extinct. In other words, are any of the *exact* HVR1 sequences considerably lower?

I only see 2 separate signatures for mtDNA I in the sample. The modal for I, and I4. Let's make sure we're not mixing apples and oranges. It's likely that many maternal branches went extinct, let's not just look at the letters.

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